Chlorine dioxide is a highly effective and safe oxidant for sterilization, deodorization, bleaching, and, for example, antistaling. Particularly, ClO2 is widely used in the food processing industry, water treatment, wood pulp manufacturing and processing, and the medical/health care industry. Very importantly, for example, chlorine dioxide is widely acknowledged to be the best and most desirable, disinfectant for water. Chlorine dioxide is listed as a Grade A1 safe disinfectant by the World Health Organization (WHO), due to its effectiveness, non-carcinogenicity and non-toxicity. Moreover, particularly in view of the physiological need of humans for safe water, as well as other materials, combined with the increasing global threat of bio-terrorism, the need for safe and efficient methods ClO2 production has now increased significantly.
An electrochemical method and two chemical methods are currently employed in the manufacturing industry to produce ClO2. The electrochemical method, i.e., Electrolytic Method, requires high capital equipment investments as well as demands high operating cost. Accordingly, very large plants are normally required to employ it. The applied Chemical methods in the industry are Chemical Oxidation and Chemical Reduction methods. The Chemical Oxidation method normally uses alkaline chlorite (mostly sodium chlorite NaClO2) as raw material. The Chemical Reduction method normally uses chlorate (mostly sodium chlorate NaClO3 or potassium chlorate KClO3) as raw materials. Since chlorate is much less expensive than chlorite, chlorate is used more widely as raw material. Between chlorate, sodium chlorate (NaClO3) is used more widely than potassium chlorate (KClO3) since NaClO3 is less expensive. Traditional reducers used in the Chemical Reduction method are SO2, Na2SO3, H2O2, NaCl, HCl, methanol, methanoic acid, oxalic acid, hydrazine sulfate and saccharose. Sodium chlorate (NaClO3) is generally employed as the raw material. H2SO4 or HCl are the most common mediums for the reaction. HCl and NaCl, for example, commonly employed as reducers, render the total amount of ClO2 and Cl2 produced as product, about 67% ClO2 and 33% Cl2. As a result, subsequent re-purification processes are then needed to enhance the purity of ClO2. In addition, the by-products are normally Na2SO4, NaHSO4 or NaCl. Many plants discharge Na2SO4 and NaHSO4 as waste materials, except for possible use as pulp treatment at some paper mills. Other traditional reducers, such as H2O2, oxalic acid, methanol, SO2 and saccharose are capable of producing ClO2 of high purity with little Cl2, but they are more expensive and difficult to employ, requiring a more complex and risky chemical process.
The invention overcomes many drawbacks of the traditional Chemical Reduction method by using a stable new reducer in a safer new chemical process. The key feature of this invention is to use Urea as the reducing agent to produce high purity ClO2.